1) Field of the Invention
The present invention relates to a technology for accurately identifying a frequency characteristic of and controlling a servo motor.
2) Description of the Related Art
A conventional method of identifying a frequency characteristic will be explained here. Such a method has been described in Japanese Patent Application Laid-Open No. 5-19858 titled xe2x80x9cservo actuatorxe2x80x9d. The frequency characteristic is identified by adding a scanned alternate signal to the instruction value of a servo system and measuring the response of the feedback control system relative to the signal added.
Precisely, a scanned signal and a speed instruction signal are superimposed and amplitude data is generated from the signals changed from the superimposed signals in a stated procedure. A resonance frequency is calculated based on this amplitude data. The resonance frequency is a frequency at which the rate of change in the amplitude data turns from positive to negative.
In the above-mentioned conventional method of identifying a frequency characteristic, the frequency characteristic is accurately identified by adding an adequate scanned signal to a speed instruction value. In other words, it is impossible to identify the correct frequency characteristic unless the scanned signal added to the speed instruction signal is appropriate.
In the conventional method, moreover, there is no reference on which to determine the amplitude of the scanned signal. Therefore, if the feedback control system is changed, it is not possible to precisely determine amplitude of scanned signal and so the frequency characteristic cannot be identified properly.
On the other hand, even if the feedback system is the same, but certain parameters are changed, then the frequency characteristic shall change. In that case, it is again not possible to determine adequate amplitude and therefore, identification of a frequency characteristic is not accurate.
The object of the present invention is to provide a method of identifying a frequency characteristic and a drive controlling apparatus that can identify a frequency characteristic accurately.
In the method and apparatus according to the present invention, an instruction value is added to a specific signal to obtain an added signal. A servo motor is driven based on this added signal. A parameter of the motor is measured while the motor is being driven. The parameter may be a response of the motor or positional information of a part of the motor. A characteristic value calculated based on the measured parameter is compared with a reference value. When the characteristic value significantly smaller than the reference value, the amplitude of the specific signal is changed so that the characteristic value converges to the reference value. When the characteristic value has almost converged to the reference value, frequency characteristics can be identified accurately.